Statistical characteristics of individual waves in laboratory wind waves I. Individual wave spectra and similarity structure

Statistical characteristics of individual waves in laboratory wind waves have been studied by use of a wind-wave tunnel. The individual waves are defined by actual undulations of the water surface at any instant, and are characterized by concentrated shearing stress and strong vorticity at their crests. A conspicuous self-similarity structure is found in the individual wave field. The similarity manifests itself as a simple spectral form, and as the statistical 3/2-power law between nondimensional wave height and wave period, and further as the -1/2-power relationship between nondimensional phase speed and frequency, for waves of the high frequency side. The normalized energy spectrum, specially defined for individual waves, has a form practically equivalent to the traditional spectrum for component waves in the main frequency range from 0.7 to 1.5 in the frequency normalized by the peak frequency, but does not have secondary peaks at harmonics. The phase speed of individual waves also coincides with that of component waves in the main frequency range.     

Vortex generation and evolution in water waves propagating over a submerged rectangular obstacle: Part I. Solitary waves

Interactions between a solitary wave and a submerged rectangular obstacle are investigated both experimentally and numerically. The Particle Image Velocimetry (PIV) technique is used to measure the velocity field in the vicinity of the obstacle. The generation and evolution of vortices due to flow separation at the corners of the obstacle are recorded and analyzed. It is found that although the size of the vortex at the weatherside of the obstacle is smaller than that at the leeside, the turbulence intensity is, however, stronger. A numerical model, based on the Reynolds Averaged Navier–Stokes (RANS) equations with a k–ϵ turbulence model, is first verified with the measurements. Overall, the agreement between the numerical results and laboratory velocity measurements is good. Using the RANS model, a series of additional numerical experiments with different wave heights and different heights of the rectangular obstacle are then performed to test the importance of the energy dissipation due to the generation of vortices. The corresponding wave transmission coefficient, the wave reflection coefficient and the energy dissipation coefficient are calculated and compared with solutions based on the potential flow theory. As the height of the obstacle increases to D/h=0.7, the energy dissipation inside the vortices can reach nearly 15% of the incoming wave energy.     

A combined wind and wave energy-converter concept in survival mode: Numerical and experimental study in regular waves with a focus on water entry and exit

A combined wind and wave energy converter concept, named STC concept was proposed. Model tests were performed in terms of operational and survival modes. Water entry and exit phenomena as well as green water on deck were observed during the survivability model tests. In this paper, a nonlinear numerical model based on a blended station-keeping potential-flow solver with a local impact solution for bottom slamming events and an approximated model for the water shipped on the deck is proposed to simulate these nonlinear phenomena. Physical investigation of the water entry and exit process was firstly carried out and uncertainty analysis of the model test results were performed. Numerical comparisons between the nonlinear solver and model test results are then performed in terms of mean, wave frequency and double wave frequency motion response components. The slamming and green water involved in the water entry process are specially investigated, in terms of the physical evolution and the effects on the dynamic motion responses. The validation work on the occurrence of slamming and water on deck as well as the slamming pressure are performed.     

Surface gravity waves from direct numerical simulations of the Euler equations: A comparison with second-order theory

When the wave spectrum is sufficiently narrow-banded and the wave steepness is sufficiently high, the modulational instability can take place and waves can be higher than expected from second-order wave theory. In order to investigate these effects on the statistical distribution of long-crested, deep water waves, direct numerical simulations of the Euler equations have been performed. Results show that, for a typical design spectral shape, both the upper and lower tails of the probability density function for the surface elevation significantly deviate from the commonly used second-order wave theory. In this respect, the crest elevation is observed to increase up to 18% at low probability levels. It would furthermore be expected that wave troughs become shallower due to nonlinear effects. Nonetheless, the numerical simulations show that the trough depressions tend to be deeper than in second-order theory.     

Comparing the passive sampler and biomonitoring of organic pollutants in water: A laboratory study

Passive sampling could provide the solution to problems associated with costly and time consuming sampling programmes and biomonitoring. Mussels (Mytilus edulis) and Chemcatcher passive sampler were simultaneously analyzed for sequestered pesticides and polychlorinated biphenyls (PCBs) by gas chromatography with mass spectrometry (GC/MSD). The Chemcatcher passive sampler based on a solid phase extraction disc with two types of diffusion-limiting membranes (polyethelene and polysulphone), were also compared. Diuron, atrazine, irgarol and lindane were accumulated in the polysulphone passive sampler in greater concentration than in the mussels or in the other passive samplers with polyethelene limiting-membrane. Mussels can accumulate in their tissue high concentration of non polar compounds such as PCB 52, dieldren and PCB 153; more than the passive sampler with polysulphone membrane. The device with polyethelene limiting membrane has high affinity capacity to concentrate high amount of phenenthrene, dieldrin, PCB 153 and PCB 52, so it acts as a sampler for non-polar compounds. The highest uptake rate of hydrophobic compounds by Chemcatcher was observed for analytes with log octanol-water partition coefficient (K_OW) between 4.5 and 7.5. Laboratory-based studies using passive samplers to assess the potential for bioaccumulation could provide robust and reliable information at relatively low cost compared to biomonitoring data. Laboratory data obtained using passive samplers could be related to accumulation under field conditions where field assessments are required.     

Detection of nonlinear waves and their contribution to ocean wave spectra Part I: Theoretical consideration

This is a Part I of a paper of nonlinearities of wind waves in the deep open ocean. First, considerations are given in order to verify the theoretical expression for bound waves from observed data. We compare the contribution of bound waves and double Bragg scattering to the second-order scattering, and we show that the contribution of bound waves is larger, and that bound waves can be detected by measuring the Doppler spectra of HF (high-frequency) radio wave scattering from the sea surface. Moreover, if the theory of the HF radio wave scattering from the sea surface is verified, so is the second-order perturbation theory for bound waves. Then, the contributions of bound waves to ocean wave spectra are investigated on the basis of the nonlinear theory. The bound waves are shown to modify frequency spectra and wave directional distributions at higher frequencies, and it is shown that although the modifications of frequency spectra are smaller for a two-dimensional field case than for a one-dimensional field case, they are not negligible at higher frequencies. On the other hand, the modifications of wave directional distributions are shown to be significant at higher frequencies. These discussions become significant only when bound wave predictions are verified in the open ocean. Consequently, it is shown that nonlinearities of water waves are important in considering both radio wave scattering from the sea surface and the detailed structures of ocean wave spectra at high frequencies.     

Three-dimensional interaction of waves and porous coastal structures using OpenFOAM®. Part I: Formulation and validation

In this paper and its companion (Higuera et al., 2014--this issue), the latest advancements regarding Volume-averaged Reynolds-averaged Navier–Stokes (VARANS) are developed in OpenFOAM® and applied. A new solver, called IHFOAM, is programmed to overcome the limitations and errors in the original OpenFOAM® code, having a rigorous implementation of the equations. Turbulence modelling is also addressed for k-ϵ and k-ω SST models within the porous media. The numerical model is validated for a wide range of cases including a dam break and wave interaction with porous structures both in two and three dimensions. In the second part of this paper the model is applied to simulate wave interaction with a real structure, using an innovative hybrid (2D–3D) methodology.     

A new scheme of nonlinear energy transfer among wind waves: RIAM method-algorithm and performance-

A numerical scheme for calculating the nonlinear energy transfer among wind waves (RIAM method) was developed on the basis of the rigorous method of Masuda. Then the performance of the RIAM method was examined by applying it to various forms of wind-wave spectra and different situations of wind-wave evolution, in comparison mainly with the WAM method. The computational time of the Masuda method was reduced by a factor of 300 by the RIAM method, which is still 2000 times slower than the WAM method simply because the RIAM method processes thousands of resonance configurations whereas the WAM method does only one. The RIAM method proves to give accurate results even for spectra of narrow band widths or bimodal spectra, whereas the WAM method often calculates an unrealistic magnitude and pattern of nonlinear energy transfer functions. In the duration-limited evolution of wind-wave spectra, the RIAM method yields a unimodal directional distribution on the low-frequency side of the spectral peak, whereas the WAM method produces a spurious bimodal one there. At higher frequencies, however, both methods give a bimodal directional distribution with two oblique maxima. The RIAM method enhances the growth of the total energy and peak period of wind waves in comparison with the WAM method. Nevertheless, Toba's constant of his 3/2-power law approaches almost the same standard value of 0.06 in both methods. For spectra of a narrow band width or for those perturbed by a small hump or depression, the RIAM method tends to recover the monotonic smoother form of spectrum whereas the WAM method often yields unrealistic humps or depressions.     

Experimental study of the Rhone plume. Part I: physics and dynamics

The complicated dynamic processes occurring when fluvial waters mix with marine waters control the nature and the fluxes of materials exported by rivers to the sea. Understanding these processes is of primary importance in evaluating budgets. In wide-open estuarine situations these processes take place under the influence of an intense turbulence induced by tides. Conversely, the Rhone waters spread into the Mediterranean Sea in the form of an easily distinguishable buoyant plume often extending far offshore from the mouth of the river. The aim of this study is to describe the dynamic and hydrological fields on the basis of eulerian VHF radar mapping of surface currents coupled with lagrangian in situ physical or geochemical measurements. This paper focuses mainly on physical processes. Data analysis provides an insight into the typical scales of variability of the phenomena, either vertically or horizontally. It is shown that morphological fluctuations can occur (mainly in orientation and offshore extent) according to wind and outflow forcing conditions, and that the vertical structure variations can range from an almost unaltered two-layer distribution to an evolving and deepening mixed layer situation, or even to a more complex superimposed multi-layered structure. The simultaneous examination of radar maps and lagrangian drifter tracking allows the main dynamic tendencies of the Rhone plume to be sketched out.     

A study of non-linear tidal propagation in shallow inlet/estuarine systems Part I: Observations

The offshore tide becomes strongly distorted as it propagates into shallow estuarine systems. Observations of sea surface elevation and horizontal currents over periods ranging from three days to one year, at nine stations within Nauset inlet/estuary, document the non-linear interaction of the off-shore equilibrium tidal constituents. Despite strong frictional attenuation within the estuary, the overtides and compound tides of M₂, S₂ and N₂, in particular, reach significant amplitude, resulting in strong tidal distortion. High frequency forced constituents in sea surface are phase-locked, consistently leading the forcing tides by 60–70°, resulting in a persistent distortion where falling tide is longer than rising tide. Forced constituents in currents are more nearly in phase with equilibrium constituents, producing flood currents which are shorter but more intense than ebb currents. A compound fortnightly tide, MS_f, modulates the mean water level such that lowest tides occur during neap phase instead of spring phase. This fortnightly tide can be contaminated by storm surge, changing the phase characteristics of this constituent. Implications of the overtides, compound tides, and lower frequency tides on near-bed, suspended and dissolved material transport are profound.     

石油类污染水体后向散射特性分析——以辽宁省盘锦市双台子河和绕阳河为例

水体悬浮物对溶解在水中的油及乳化油有吸附作用,这种作用会叠加在颗粒物上,对水体的后向散射系数产生影响,而水体后向散射系数是水色遥感的重要参数之一,对建立遥感反演石油类污染浓度半分析模型起着关键性的作用。根据2008年5月在辽宁省盘锦市辽河油田境内双台子河和绕阳河现场测定的水样,对水体组分进行浓度分析,并分别利用分光光度计及后向散射系数测量仪测定水色三要素的吸收系数和水体后向散射系数。根据获取的数据,对石油类污染水体后向散射特性进行分析,分别建立了(1)石油类污染水体后向散射系数光谱模型;(2)石油类污染水体和非石油类污染水体后向散射系数与无机悬浮物浓度的关系模型。研究结果表明:(1)在建立的后向散射系数光谱模型中,幂函数指数平均值为0.87;(2)从相关系数分析来看,对后向散射系数起主要作用的是无机悬浮物浓度,其次是石油类物质浓度,而有机悬浮物浓度几乎没有影响;(3)对于无石油类污染水体,后向散射系数与无机悬浮物浓度为对数关系模型,而与有石油类污染水体更接近线性关系模型。     

A troposphere–stratosphere–mesosphere general circulation model with parameterization of gravity waves: climatology and sensitivity studies

The climatology of the troposphere–stratosphere–mesosphere model of the Institute for Numerical Mathematics (INM) with the uppermost level at 0.003 hPa is presented. This model is vertically extended from the upper level of 10 hPa for the earlier version, and a drag parameterization due to internal gravity waves (GW) is included. The model describes the main features of the mesospheric circulation: decreasing and reversion of westerly and easterly winds, equatorward shift of the westerly wind maximum with height and reversal of the meridional temperature gradient in the upper mesosphere. The model underestimates to some extent the amplitude of wave number 1 for stationary waves in the winter hemisphere. The same holds for the internal low‐frequency variability in the winter stratosphere. The sensitivity of the model climate is studied with respect to the inclusion of orographic gravity wave drag and the variation of the source height of internal gravity waves.     

A numerical study of the relative importance of wind and topographic forcing on oceanic eddy shedding by tall, deep water islands

A process-oriented, quasi-geostrophic, barotropic model has been developed with the aim of studying the relative importance of wind and topographic forcing on oceanic eddy generation by tall, deep water islands. As a case study, we chose the island of Gran Canaria. Topographic forcing was established using different intensities (weak, medium, strong, and very strong) for the oceanic current incident to the island. Wind forcing was introduced to simulate the mean wind curl observed in atmospheric tall island wakes. As observed from in situ data, the resulting wind curl consists of two cells of opposite sign which become a complementary source of vorticity at the island lee. The intensity and the shape of the two cells depend on the strength of the incident wind against the obstacle. The oceanic model was forced at three different wind (trade winds) speeds which correspond to weak, medium and strong wind intensities. Results from several numerical experiments show that in those periods where the incident wind is in the medium–strong range and the incident current speed is low (low Reynolds number), the wind forcing is the trigger mechanism for oceanic eddy generation. Eddies are spun off from the island for a lower Reynolds number (Re)/intensity of the oceanic flow (Re = 20) when compared with only topographic forcing (Re > 60). However, when the current speed is strong (high Reynolds number), the vorticity input by the wind is quickly advected by the oceanic flow and does not contribute to oceanic eddy generation. When only wind forcing is considered, only two stationary eddies are generated in the island wake. In this case, eddies of opposite sign are not sequentially spun off by the island and a Von-Kármán-like eddy street is not developed downstream of the island. Therefore, the main mechanism responsible for the development of an eddy street is the topographic perturbation of the oceanic flow by the island flanks. The wind over the island wake acts only as an additional source of vorticity, promoting the generation of an eddy street at a lower intensity of the incident oceanic flow, but not being capable of generating an eddy street without the topographic forcing.     

A study into the export of saline water from Hervey Bay, Australia

Australia's climate is one of the world's driest and locally characterised by high year-to-year rainfall variability. Due to high evaporation and low river runoff many estuaries and embayments in the region are characterised by inverse conditions with salinity increasing toward the coast and river mouths. Such conditions were also found during the first comprehensive hydrographic survey of Hervey Bay located at the east coast of Australia in early spring 2004. The survey traced a subsurface salinity maximum that was found in earlier studies within the East Australia Current, east of Hervey Bay to the shallow southwest regions of the bay. These are identified as the most likely source region for locally produced saline Hervey Bay Water. Utilising a simple box model, mean evaporation rates and historical river runoff data, it is demonstrated that inverse conditions are likely to dominate throughout the year. The negative circulation is a climatological feature of this estuary that is not limited to the dry season of the year. Due to persistent drought and declining rainfall in coastal eastern Australia, these conditions are likely to persist into the near future and need to be considered in coastal management strategies.     

南极中山站夏季下降风数值模拟个例研究

南极内陆地面辐射冷却产生的近表层冷空气,沿高原斜坡向下流动而形成下降风,其分布形态决定了南极大陆近表层风场的主要特征。我国南极中山站全年均受下降风的强烈影响。夏季晴天时,中山站的下降风一般在傍晚开始出现,风速在午夜达到极值,在次日中午之前逐渐减弱,风速有显著的日循环特征。本文选取南极中山站2010年1月的夏季下降风个例,使用常规地面气象观测资料和Polar WRF极地大气数值模式进行了分析研究。结果表明:中山站夏季夜间晴天出现偏东向的下降风时,近地面风速变化趋势与地面气温呈负相关,相关系数为-0.91。数值模拟发现,中山站下降风在距地面高度约100~150 m之间时风速最大,约为15~21 m/s。在下降风发生时,近地层大气存在逆温现象。下降风较强时,近地层逆温也较强,逆温层厚度约为200~300 m,逆温强度约为4~6℃。在地面摩擦的作用下,中山站近地面下降风风向为东南,随着高度的增加,风向逆时针偏转,最终趋于与地形等高线平行。没有太阳直接辐射时,南极大陆地区存在持续的逆温层,逆温层的出现加强了下降风气流,随着逆温的增强,大风区逐渐西移,且面积不断增加。在夏季太阳辐射造成的逆温消失的短暂时间内,逆温时产生的下降风尚不能完全消失,由此形成了较稳定的风向空间分布特征。     

海洋测绘学科体系研究(一):总论

海洋测绘学是一门研究海洋地理空间信息获取、处理、表达、管理和应用的综合性学科.介绍了海洋测绘学科发展概貌与内涵特点,梳理分析了当前测绘学科分类现状与存在问题,设计构建了海洋测绘学科体系架构,阐述了海洋测绘学科专业构成、概念定义与研究重点,为海洋测绘学科建设发展研究提供基础知识与理论参考.     

A numerical study on the role of wind forcing,bottom topography,and nonhydrostacy in coastal upwelling

The responses of coastal upwelling to different magnitudes of wind stress over a narrow and a wide shelf are studied using a 3-D primitive equation numerical model. The results show that the position of the upwelling front depends on both the strength and the duration of the wind forcing. The comparison between different shelf widths shows that wide shelf will limit the cold water intrusion, so that the corresponding decrease in sea surface temperature is less compared to narrow shelves. Besides, the difference between hydrostatic and nonhydrostatic model results shows that nonhydrostatic effects will enhance the growth of surface meandering, and can be more pronounced near steep fronts. Although difference does exist, our results show that the nonhydrostatic effects are very small at least in this idealized study case.     

A derivation of the scaling law, the power law and the scaling relation for fetch-limited wind waves using the renormalization group theory

A state of wind waves at a fetch is assumed to be transformed into another state of wind waves at a different fetch by the renormalization group transformation. The scaling laws for the covariance of water surface displacement and for the one-dimensional and two-dimensional spectrum and the power law for the growth relation are derived from the fact that the renormalization group transformation constitutes a semigroup. The scaling relation or the relation among the exponents of the power law is also derived, using the two assumptions that the renormalization group transformation is applicable to fetch-limited wind waves and that the saturated range exists, which implies that the directional distribution function of energy in the wave number region much larger than the peak wave number does not depend on wave number.